The invention relates to a method for detecting a leak in a crankcase breather of an internal combustion engine, in which crankcase breather a cavity of a crankcase is connected in a gas-conducting manner to a fresh air section of the internal combustion engine, and a pressure sensor is provided for measuring a pressure in the cavity or the crankcase breather or in a cylinder head of the internal combustion engine.
Crankcase gases can contain multiple hydrocarbon concentrations with respect to the exhaust gases of the internal combustion engine. Monitoring systems, such as a crankcase breather, feed these crankcase gases to the intake system of the internal combustion engine at a suitable point, as a result of which the gases are fed to the combustion. Whereas in earlier years the crankcase gases were usually let out untreated into the ambient air, nowadays the venting of the crankcase is generally legally prescribed. So that the crankcase gases which are enriched with hydrocarbons cannot pass unchecked into the ambient air, a method for detecting a leak in a crankcase breather is proposed.
With respect to the technical field of a crankcase breather, reference is made, for example, to German laid-open patent application DE 10 2008 002 721 A1. This laid-open patent application discloses a method for checking the functional capability of a crankcase breather system of an internal combustion engine for a vehicle. The method has following steps:
1) interrupting the venting line between the crankcase and the air feed system of the internal combustion engine during a checking time period;
2) determining the change in an operating parameter of the internal combustion engine during the checking time period; and
3) detecting a fault in the crankcase breather system on the basis of the determined change in the operating parameter.
This method for detecting a leak in a crankcase breather does not have any significant disadvantage but is relatively time-consuming.
German laid-open patent application DE 10 2010 027 117 A1 also discloses a method and a system for monitoring a satisfactory connection of a crankcase breather system between a valve cover and an inlet system. The method includes detecting the electrical continuity between a hose connector at one end of a hose and an inlet system connector which can be mechanically connected to the hose connector.
It is disadvantageous that the entire system is relatively costly.
Furthermore, German laid-open patent application DE 100 26 492 A1 also discloses a method for performing functional diagnostics of a breather system of a crankcase of an internal combustion engine, in which method a cyclically operated valve is arranged in a venting line. The cyclically operated valve is controlled as a function of the pressure in the crankcase, which pressure is sensed by a pressure sensor. In the case of high pressure, the cyclically operated valve is opened in order to be able to suck the crankcase vapors out via the intake manifold. The cyclically operated valve is controlled here as a function of operating requests, exhaust gas requests and/or load states. On the basis of the pressure profile it is possible to detect whether, for example, the oil level is sufficient, there is a leak in the closed breather system or the internal combustion engine has increased wear.
The indirect actuation of the cyclically operated valve by means of the pressure sensor is disadvantageous.
Furthermore, it is a legal requirement for the US market that hoses which conduct crankcase gases are non-releasable or, if they can be released, are detected by way of an OBD (on-board diagnostics) if they are not plugged in. At present, hoses which are not plugged in are usually detected by comparing different engine mass flows or by means of mixture diagnostics. In this context, the engine mass flow is measured by use of a hot-film air mass flow meter (HFM).
A disadvantage with these known systems is that the selectivity between a satisfactory system and a faulty system is not always sufficient. Furthermore, an expensive hot-film air mass flow meter is required.
The object of the present invention is to provide a method for detecting a leak in a crankcase breather which requires minimum structural expenditure.
This and other objects are achieved by a method for determining a leak in a crankcase breather of an internal combustion engine, in which crankcase breather a cavity of a crankcase is connected in a gas-conducting manner to a fresh air section of the internal combustion engine, and a pressure sensor is provided for measuring a pressure in the cavity or the crankcase breather or in a cylinder head of the internal combustion engine. An electronic control unit is provided for evaluating the signals of said pressure sensor, wherein the method includes the following acts: measuring a gas pressure with the pressure sensor in the crankcase breather system at a defined rotational speed and load of the internal combustion engine; comparing an actual pressure value with a setpoint pressure value; and detecting a leak when the setpoint pressure value is exceeded.
In the cavity in the crankcase, there is a significant underpressure with respect to the surroundings in the lower and in the very high load and rotational speed ranges. In order to detect a leak in the crankcase breather system, a comparison of the air pressure in the crankcase can be measured in these load/rotational speed ranges with a pressure sensor, which is present in any case, and compared with a limiting value which is stored, for example, in a control unit. Therefore, a crankcase breather system which is subject to a leak can easily be detected. As a result of this method according to the invention, the need for a hot-film air mass flow meter can be advantageously avoided, while at the same time very good selectivity between a satisfactory system and a defective system is obtained.
Advantageous developments of the method according to the invention are described herein.
Therefore, according to a preferred embodiment a leak is preferably detected if the actual pressure value is at least 10% above the setpoint pressure value.
The setpoint pressure value is to be particularly preferably read out from a characteristic diagram which is stored in a control unit.
During the detection of a leak, the rotational speed of the internal combustion engine during the pressure measurement is preferably between 500 l/min and 5000 l/min, and in particular between 500 l/min and 3000 l/min.
Furthermore, a load of the internal combustion engine during the pressure measurement is preferably between 10% and 100%, and in particular between 20% and 40% of a maximum load, if the internal combustion engine does not have a supercharger device such as, for example, an exhaust gas turbocharger.
A load of the internal combustion engine during the pressure measurement is also preferably between 10% and 150%, and in particular between 20% and 80% of a maximum load, if the internal combustion engine has a supercharger device such as, for example, an exhaust gas turbocharger and/or a compressor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.